Merge pull request #1097 from anthrotype/py23-redirect-stream

[py23] Add backports for redirect_stdout/stderr context managers

Lib/fontTools/misc/py23.py

@@ -496,6 +496,53 @@ except ImportError:
 			return self.__dict__ == other.__dict__
 
 
+if sys.version_info[:2] > (3, 4):
+	from contextlib import redirect_stdout, redirect_stderr
+else:
+	# `redirect_stdout` was added with python3.4, while `redirect_stderr`
+	# with python3.5. For simplicity, I redefine both for any versions
+	# less than or equal to 3.4.
+	# The code below is copied from:
+	# https://github.com/python/cpython/blob/57161aa/Lib/contextlib.py
+
+	class _RedirectStream(object):
+
+		_stream = None
+
+		def __init__(self, new_target):
+			self._new_target = new_target
+			# We use a list of old targets to make this CM re-entrant
+			self._old_targets = []
+
+		def __enter__(self):
+			self._old_targets.append(getattr(sys, self._stream))
+			setattr(sys, self._stream, self._new_target)
+			return self._new_target
+
+		def __exit__(self, exctype, excinst, exctb):
+			setattr(sys, self._stream, self._old_targets.pop())
+
+
+	class redirect_stdout(_RedirectStream):
+		"""Context manager for temporarily redirecting stdout to another file.
+			# How to send help() to stderr
+			with redirect_stdout(sys.stderr):
+				help(dir)
+			# How to write help() to a file
+			with open('help.txt', 'w') as f:
+				with redirect_stdout(f):
+					help(pow)
+		"""
+
+		_stream = "stdout"
+
+
+	class redirect_stderr(_RedirectStream):
+		"""Context manager for temporarily redirecting stderr to another file."""
+
+		_stream = "stderr"
+
+
 if __name__ == "__main__":
 	import doctest, sys
 	sys.exit(doctest.testmod().failed)

Tests/misc/py23_test.py

@@ -8,7 +8,8 @@ import sys
 import os
 import unittest
 
-from fontTools.misc.py23 import round2, round3, isclose
+from fontTools.misc.py23 import (
+	round2, round3, isclose, redirect_stdout, redirect_stderr)
 
 
 PIPE_SCRIPT = """\
@@ -418,5 +419,67 @@ class NarrowUnicodeBuildTest(unittest.TestCase):
 		self.assertEqual(byteord(u'\U0010FFFF'), 1114111)
 
 
+class TestRedirectStream:
+
+    redirect_stream = None
+    orig_stream = None
+
+    def test_no_redirect_in_init(self):
+        orig_stdout = getattr(sys, self.orig_stream)
+        self.redirect_stream(None)
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+
+    def test_redirect_to_string_io(self):
+        f = StringIO()
+        msg = "Consider an API like help(), which prints directly to stdout"
+        orig_stdout = getattr(sys, self.orig_stream)
+        with self.redirect_stream(f):
+            print(msg, file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+        s = f.getvalue().strip()
+        self.assertEqual(s, msg)
+
+    def test_enter_result_is_target(self):
+        f = StringIO()
+        with self.redirect_stream(f) as enter_result:
+            self.assertIs(enter_result, f)
+
+    def test_cm_is_reusable(self):
+        f = StringIO()
+        write_to_f = self.redirect_stream(f)
+        orig_stdout = getattr(sys, self.orig_stream)
+        with write_to_f:
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
+        with write_to_f:
+            print("World!", file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+        s = f.getvalue()
+        self.assertEqual(s, "Hello World!\n")
+
+    def test_cm_is_reentrant(self):
+        f = StringIO()
+        write_to_f = self.redirect_stream(f)
+        orig_stdout = getattr(sys, self.orig_stream)
+        with write_to_f:
+            print("Hello", end=" ", file=getattr(sys, self.orig_stream))
+            with write_to_f:
+                print("World!", file=getattr(sys, self.orig_stream))
+        self.assertIs(getattr(sys, self.orig_stream), orig_stdout)
+        s = f.getvalue()
+        self.assertEqual(s, "Hello World!\n")
+
+
+class TestRedirectStdout(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stdout
+    orig_stream = "stdout"
+
+
+class TestRedirectStderr(TestRedirectStream, unittest.TestCase):
+
+    redirect_stream = redirect_stderr
+    orig_stream = "stderr"
+
+
 if __name__ == "__main__":
 	sys.exit(unittest.main())